The present patent application claims priority to co-pending Japanese Application No. 2001-097183, filed on Mar. 29, 2001.
1. Technical Field
The present invention relates to direct access storage devices in general, and in particular to hard disk drives. Still more particularly, the present invention relates to a method for controlling write current to a write head during data write on a hard disk drive.
2. Description of the Related Art
A hard disk drive is one of the most prevailing direct access storage devices for data processing systems. A hard disk drive is provided with a combined magnetic head that includes a read head for reading data from a magnetic disk, and a write head for writing data to the magnetic disk. The magnetic head is coupled to an actuator mechanism to be moved and positioned by a voice coil motor. The actuator mechanism moves and positions the magnetic head to a predetermined track for reading or writing data. The moving-and-positioning operation is referred to as a seek operation.
In order to write data in a magnetic disk by a magnetic head, a magnetic layer formed on the magnetic disk is magnetized by supplying a predetermined amount of current to the write head. New data is frequently written over previously written data of the magnetic disk. Such process is referred to as overwrite. The overwrite characteristic showing whether overwrite is properly performed depends on a write current value for writing data by the write head. It is generally known that the overwrite characteristic is deteriorated because the magnetized pattern of previously written data cannot be completely re-magnetized when the write current value is too small. However, when the write current value is too large, a squeeze phenomenon occurs that can affect magnetized patterns of adjacent tracks. Moreover, the characteristic of a read signal is also frequently deteriorated. Therefore, it is necessary to set the write current value to a proper value.
An optimum write current value is not univocally decided. For example, it is known that overwrite performance is affected by the environment in which a hard disk drive is placed. Because the coercivity (Hc) of the magnetic film of a magnetic disk rises as temperature lowers, the overwrite characteristic deteriorates as temperature lowers, under a constant write current value. In addition, a hard disk drive is frequently provided with multiple magnetic disks and several magnetic heads corresponding to the number of storage faces of the magnetic disks. The overwrite characteristic may differ from magnetic disks and magnetic heads. In other words, the overwrite characteristic may differ for each combination of magnetic disks and magnetic heads due to the fluctuation in each magnetic head and magnetic disk. Furthermore, the overwrite characteristic fluctuates according to the location of a magnetic head, such as on an inner track or an outer track. Specifically, it is known that the overwrite characteristic is worse on an outer track of a magnetic disk because the data write speed is higher for the outer track.
There are various prior art methods for controlling the overwrite characteristic of a hard disk drive. For example, the method disclosed in Published Unexamined Japanese Patent Application No. 2000-222703 is effective for controlling the fluctuation in overwrite performance due to an environmental temperature. Published Unexamined Japanese Patent Application No. 2000-222703 discloses the art for setting a write current value according to an operating environment temperature of a hard disk drive and a magnetic head-magnetic disk combination. In addition, as for the overwrite characteristic differs for each magnetic head-magnetic disk combination, Published Unexamined Japanese Patent Application No. 1995-14107 discloses the art for automatically setting an optimum write current value for each magnetic head-magnetic disk combination. Furthermore, as for the overwrite characteristic fluctuates at an inner track and an outer track of a magnetic disk, Published Unexamined Japanese Patent Application No. 1996-96309 discloses the art for decreasing a write current value at an inner track and increasing a write current value at an outer track of a magnetic disk.
The overwrite characteristic has been somewhat improved by optimizing a write current value using some or all of the above-mentioned prior art. However, it is still preferable to have a better method for further optimizing a write current value corresponding to improvement of a recording density, and a flying height value of a magnetic head according to the improvement of the recording density. Consequently, it would be desirable to provide a method to improve the overwrite characteristic by controlling the supply of write current to a write head when writing data on a hard disk drive.
In accordance with a preferred embodiment of the present invention, a direct access storage device includes a rotating storage medium in which data are magnetically written, a write head for writing data in the rotating storage medium, and a write current control circuit for changing write current-value settings to be supplied to the write head according to a predetermined elapsed time from the beginning of a write operation.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.